Additional time series simulations

[rmehta004]

• Implement the following simulations in the mgcpy\benchmarks\ts_benchmarks.py. You can find other examples in that file. Result is an [n*d] matrix that‘s number of timesteps by number of dimensions.
• There are really basic unit tests in mgcpy\benchmarks\unit_tests. Either mirror these tests, or think of better ones to test them.
• PR to time-series branch of https://github.com/neurodata/mgcpy. There are 3 simulations to be added.
• Extinct Gaussian from Section 4, Paragraph “Non-linear dependence.” from https://arxiv.org/pdf/1402.4501.pdf. There should be an extinction rate parameter.
• The econometric process from Section 5 Paragraph “Lag-HSIC” from https://arxiv.org/pdf/1408.5404.pdf.
• The dynamic process from Section 5 Paragraph “Lag-HSIC” from https://arxiv.org/pdf/1408.5404.pdf.